Apparatus utilizing an air core transformer for determining magnetic material content of a substance

ABSTRACT

An air-core transformer is adapted to receive a sample of the substance to be tested for content of magnetic material, e.g., the mineral magnetite. It is supplied, usually through loadisolating means, with constant voltage, high frequency, A.C. power from a square wave generator or the like, preferably a multi-vibrator receiving voltage-regulated D.C. power from a suitable power supply. The resulting high frequency A.C. signal is detected by passage through rectifying and filtering means to yield a corresponding D.C. signal, which is fed to amplifying means that includes means for compensating for non-linearity of the signal. The compensated and amplified D.C. signal is zero controlled and fed to read-out means, such as a meter, through suitable range control means.

United States Patent Walter [541 APPARATUS UTILIZING AN AIR CORE TRANSFORMER FOR DETERMINING MAGNETIC MATERIAL CONTENT OF SAMPLE CONTAINING OR BELIEVED TO CONTAIN MAGNETITE AIR CORE TRANSFORMER A, C. SIGNAL DETECTOR (RECTIFIER AND FILTER) D, C. SIGNAL AMPLIFIER 5] 3,686,563 Aug. 22, 1972 Primary Examiner-Gerard R. Strecker Attorney-John L. Sniado and Mallinckrodt & Cornaby [5 7] ABSTRACT An air-core transformer is adapted to receive a sample of the substance to be tested for content of magnetic material, e.g., the mineral magnetite. It is supplied, usually through load-isolating means, with constant voltage, high frequency, AC. power from a square wave generator or the like, preferably a multi-vibrator receiving voltage-regulated DC. power from a suita ble power supply. The resulting high frequency A.C. signal is detected by passage through rectifying and filtering means to yield a corresponding DC. signal, which is fed to amplifying means that includes means for compensating for non-linearity of the signal. The compensated and amplified DC. signal is zero controlled and fed to read-out means, such as a meter, through suitable range control means.

5 Claims, 5 Drawing Figures MULTlVlBRATOR DIFFERENTIATING MEANS LOAD ISOLATOR COMPENSATION FOR NO -LlNEARlTY OF SIGNAL) COMPENSATED AND AMPLIFIED D. C. SIGNAL Patented Aug. 22, 1972 3,686,563

5 Sheets-Sheet l /6 9 Ti/2 /40 w SAMPLE CONTAINING OR BELIEVED TO CONTAIN MAGNETITE MULTIVIBRATOR AIR CORE I TRANSFORMER DIFFERENTIATING MEANS A. C. SIGNAL LOAD ISOLATOR DETECTOR (RECTIFIER AND FILTER) D. C. SIGNAL ZERO ADLIFUST CIRCUI AMPLIFIER (COMPENSATION FOR NON-LINEARITY OF SIGNAL) SOLID STATE D. C. POWER COMPENSATED AND SUPPLY AMPLIFIED D. C. SIGNAL IIO-IZOV METER RANGE CONTROL A. C. LINE READ-OUT METER INVENTOR. KENNETH E. WALTER ATTORNE YS Patented Aug. 22, 1972 3,686,563

5 Sheets-Sheet 5 55 so MAGNETITE METER READING INVENTOR.

KENNETH E. WALTER ATTORNEYS BACKGROUND OF THE INVENTION 1. Field The invention is in the field of electrical apparatus for measuring the magnetic material content of various materials, particularly mineral materials, such as ores and slags, containing or believed to contain magnetite.

State of the Art A variety of types of electrical apparatus for determining the magnetite material content of ores and ore materials have been developed heretofore. Although some of these have been designed to be portable, those using iron-core transformers have been heavier than desirable and all have left something to be desired in terms of stability and sensitivity.

SUMMARY OF THE INVENTION In accordance with the present invention an air-core transformer, having primary and secondary coils wound about a magnetically inert carrier recessed centrally to receive a sample of the material to be tested, is connected in electrical circuit with a constant voltage D.C. power supply through a square wave generator and, if required, a load isolator. Thus, the transformer receives high frequency A.C. power that is not subject to line voltage fluctuations.

An A.C. signal from the transformer, constituting, in effect, a measurement directly proportional to the amount of magnetic material in the sample, is passed through detector means for rectification and filtering to produce a corresponding D.C. signal, which is then passed through an amplifier provided with means in its feedback circuitry for compensating for nonlinearity of the signal. The detector means advantageously comprises a diode arranged in circuit with resistance and capacitance. The means in the amplifier feedback circuit compensating for signal nonlinearity advantageously comprises transistor circuitry.

Since even without a sample in the core of the transformer there is some coupling between the primary and secondary, provision is made to adjust for the inevitable small D.C. leakage taking place, so the system will be zero calibrated. The means to accomplish this advantageously comprises a potentiometer circuit.

For readout of magnetic material content of samples tested, a meter, oscilloscope, recorder, etc., could be employed. It is preferred to utilize a meter having a range of to 25 microamps, so the amplifier need provide only for moderate gain, and to employ a range control device utilizing a series of resistors that can be selectively brought into circuit, as by push buttons.

THE DRAWINGS A specific embodiment of apparatus constituting the best mode presently contemplated of carrying out the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a view in front elevation of the apparatus in preferred console arrangement for convenient handling as portable instrumentation for the intended purpose;

FIG. 2, a fragmentary view in vertical section taken on the line 22 of FIG. 1 and drawn to a larger scale;

FIG. 3, a block diagram descriptive of the system;

FIG. 4, a wiring diagram of the preferred circuitry; and

FIG. 5, specimen calibration curves for use with meter readings to determine percent magnetite in an ore sample.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT In the form illustrated, the apparatus is mounted in a console housing 10, FIG. 1, provided with an electrical cord plug-in connection 11 for a standard electrical receptacle supplying A.C. power of 1 10-120 volts from the usual line source. A readout meter 12 is mounted in a suitable aperture in the front panel of housing 10, and various utility and operating facilities are grouped around its exposed face, as shown, including an opening 13 leading into the hollow core of an air-core transformer 14, FIG. 2, that is suitably mounted within housing 10. In use, samples of material containing or thought to contain magnetic constituents, such as the mineral magnetite, are inserted into and removed from the transformer core 14a by way of opening 13.

The circuitry within housing 10 includes the various components indicated in FIG. 3 interconnected as shown in FIG. 4.

Air-core transformer 14 comprises primary and secondary coils 14b and 14c, respectively, wound in separate channels on a carrier 14d of magnetically inert material which defines sample-receiving air core 14a.

Power is supplied the system from the usual electrical supply lines by plugging cord 1 1 into outlet tenninal connections 15, FIG. 4. It travels to sample transformer 14 by way of a manually controlled on-off switch 16, a D.C. power supply 17, a square wave generator in the form of a multivibrator circuit 18, a differentiating capacitor 19, and a load isolator circuit 20.

It should be noted that load isolation is not required if the square wave generator has drive capability sufficient to maintain constant frequency under varying load conditions in the transformer due to varying quantities of magnetic material in the sample. Ordinarily, load isolation is advisable.

As illustrated, D.C. power supply 17 comprises dual- Zener regulated, negative and positive supplies 17a and 17b, respectively, of 10 volts each, and two triple- Zener regulated, positive supplies 17c and 17d, respectively, of 4.3 volts and 6.2 volts. Direct current for-the Zener diodes employed in 17a is provided by a full wave rectifier circuit 17c and for the Zener diodes employed in 17b, 17c, and 17d by a full wave rectifier circuit 17 f. Although this type of power supply is preferred, other types such as a series transistor regulated voltage power supply could be used to achieve essentially the same results.

Multivibrator circuit 18 of the present embodiment comprises a logic element 18a of standard usage, wired to perform as a multivibrator. The pin number designations are of a Fairchild Type 914 Dual 2-input gate. Diode 18b is for temperature compensation and the entire circuit provides a free running multivibrator of approximately 3 kilocycles. It should be noted that a frequency of at least 2 or 3 kc enables the use of an airtion circuit 20. As shown, circuit 20 comprises transistor 20a and resistors 20b, 20c, and 20d connected to function as an emitter follower isolating the load from the signal source. Load isolation is desirable in most instances to prevent pulling of the signal source frequency due to changing load conditions in the sample transformer. Such pulling would introduce undesirable nonlinearities into resulting calibration curves.

The secondary 140 of sample transformer 14 is connected to a detector circuit 21, which rectifies and filters the transmitted A.C. signal and passes a resultant DC signal on to amplifier circuitry 22 provided with means 22a to compensate for signal nonlinearity. A resistor 23 and capacitor 24 in transformer circuit 14 are provided to dampen oscillations in the secondary. It should be noted that transformer 14 provides signal source coupling to detector 21 which is directly proportional to the magnetic material content of the sample being tested.

Amplifier circuitry 22 is of any standard type, e. g., as shown. The means 22a compensating for signal nonlinearity is, in this instance, a transistor serving as a nonlinear element in the amplifier feedback circuit which approximately counteracts the nonlinearity introduced by diode 21a of detector circuit 21. Gain and slope controls 22b and 220, respectively, are provided in the amplifier circuitry. Power for the amplifier comes directly from power supply 17 as indicated in the wiring diagram of FIG. 4.

A zero-adjust circuit 25, receiving its power from power supply 17, feeds a compensating DC. signal into amplifier 22d. This enables the operator to offset the small D.C. leakage current that passes from primary to secondary of transformer 14 even though no sample is present in core 14a thereof. Thus, an initial zero setting on meter 12 is obtainable. Circuit 25 is a potentiometer utilizing standard resistors in a conventional arrangement, as shown in FIG. 4, and controlled at 25a.

To enable the use of a sensitive readout meter, e.g., one having a scale reading from to 25 microamps, it is advantageous to provide for range control of the output signal. For this purpose, meter range control means 26 is provided, comprising a plurality of push-button switches 26a, respectively, arranged, along with respective sets 26b of resistors, in electrical parallel to enable selection of one or another range for the meter at any given time.

In operation, the material to be tested will usually be a sample of crushed and finely ground ore or slag in a free-flowing, dry state. As such, the sample will be placed in a vial made of some magnetically inert material, e.g., a plastic, dimensioned to fit closely into core 14a. Power switch 16 will be turned on and the system left for a period of at least minutes for warmup. Thereafter, meter range button No. 1 will be pressed and held down while zero-adjust knob 25a is turned until the pointer of meter 12 rests at O on the readout scale. The meter range button will then be released and the sample vial inserted in transformer core 14a by way of access opening 13.

Following insertion of the sample, assuming it to be material containing or believed to contain magnetite, meter range button No. 4 should be pressed. If the meter reading is above 15, No. 4 calibration curve,

FIG. 5, is to be consulted for percent magnetite. If the meter reading is below 15, meter range button No. 3 should be pressed to obtain a reading above 15 for use with calibration curve No. 3. If the meter reading is still below 15, meter button No. 2 should be pressed to obtain a reading above 10 for use with calibration curve No. 2. If the meter reading is below 10, meter range button No. 1 should be pressed. Since meter range No. 1 is linear, percent magnetite can be read directly from the meter scale.

It should be noted that a corrective factor must be applied to meter readings depending upon system warm-up time. Thus, readings will be 1.3 percent too high after a 10 minute warm-up; 0.8 percent too high after 30 minute warm-up; and 0.4 percent too high after 60 minute warm-up.

Care should be taken in sample preparation. Thus, for best results, the material to be analyzed should be ground in a nonmetallic grinder, such as a ceramic pebble mill. If a common iron ball grinder is used, there will be from 2 to 4 percent iron contributed to the sample from the grinder. The fineness of grind should be mesh. Packing of the ground sample is very important. A reading lower than the actual magnetite content will be obtained if the sample is not packed very tightly. A slightly higher than true reading will be obtained if the material is packed too tightly. This error is much smaller than that which will result if the sample is not packed firmly enough. A funnel and tamping tool of plastic or other magnetically inert material should be used for packing the ground sample material into the via]. The funnel should be placed in the vial, which should be set on a firm surface. The vial should be filled about one-fourth of its capacity and then tamped to about three-sixteenths of its capacity, this procedure being repeated until the vial is filled to just over the top. The material should be leveled off the top and the cap of the vial firmly and completely seated on the upper rim of the via].

The calibration curves are prepared by inserting samples of known magnetite content, in terms of percent by weight, mixed with more or less of a magneti- I cally inert material, such as a pure silica sand.

The system can be battery powered, in which event the power supply circuitry 17 will be replaced by a battery with voltage regulating circuitry of known type.

Whereas this invention is here illustrated and described with respect to certain preferred forms thereof, it is to be understood that many variations are possible without departing from the inventive concepts particularly pointed out in the claims.

I claim:

1. Apparatus for determining the magnetic material content of a substance, comprising: Y

an air-core transformer adapted to receive, in its core, a sample of the said substance;

a constant voltage DC. power supply for the apparatus;

square wave generator means and means for differentiating the generated square wave interconnected between said power supply and said transformer for converting DC. power to high frequency AC. power for the transformer;

detector means for rectifying and filtering A.C.

signals from the transformer to produce corresponding D.C. signal output;

means for amplifying said DC. signal output, including means for compensating for nonlinearity of the signal;

zero control means for the amplified signal; and

readout means controlled by the amplified and zero- 5 controlled signal.

2. Apparatus in accordance with claim 1, additionally including range control means for said readout means.

3. Apparatus in accordance with claim 2, wherein the readout means is a sensitive microammeter and the range control means comprises a plurality of sets of resistors and switches, said sets being interconnected in 

1. Apparatus for determining the magnetic material content of a substance, comprising: an air-core transformer adapted to receive, in its core, a sample of the said substance; a constant voltage D.C. power supply for the apparatus; square wave generator means and means for differentiating the generated square wave interconnected between said power supply and said transformer for converting D.C. power to high frequency A.C. power for the transformer; detector means for rectifying and filtering A.C. signals from the transformer to produce corresponding D.C. signal output; means for amplifying said D.C. signal output, including means for compensating for nonlinearity of the signal; zero control means for the amplified signal; and readout means controlled by the amplified and zero-controlled signal.
 2. Apparatus in accordance with claim 1, additionally including range control means for said readout means.
 3. Apparatus in accordance with claim 2, wherein the readout means is a sensitive microammeter and the range control means comprises a plurality of sets of resistors and switches, said sets being interconnected in electrical parallel.
 4. Apparatus in accordance with claim 1, additionally including means for isolating the transformer load from the oscillator, resulting in a constant voltage A.C. signal output independent of the magnetic content of the sample in all instances of use of the apparatus.
 5. Apparatus in accordance with claim 4, wherein the load isolation means comprises solid state circuitry including a transistor and resistors connected to function as an emitter follower. 